How to find factorial of 25 in javascript

Question

When I used

function processData(input) {`console.log(fact(input));`}

function fact(input) {
  if (input == 1 || input == 0) {
    return input;
  } else {
    return input * fact(input - 1);
  }
}

I get output is:

1.5511210043330986e+25

but I need :

15511210043330985984000000

what I do for This output. I am not able to include any library because it was online test and I don't have permission to add libraries.

http://stackoverflow.com/questions/20001325/convert-big-number-to-string-without-scientific-notation — Ramesh Kotha, Aug 15 '15 at 19:37
You have the correct output -- the value `1.5511210043330986e+25` is the same as `15511210043330985984000000`, but displayed in scientific notation format. — Spudley, Aug 15 '15 at 19:39
yes but i need 15511210043330985984000000 instead of 1.5511210043330986e+25. — Nitesh singh, Aug 15 '15 at 19:57
a library is needed because the number being used is larger than `Number.MAX_SAFE_INTEGER`. — WhiteHat, Aug 15 '15 at 19:59
when i use http://stackoverflow.com/questions/20001325/convert-big-number-to-string-without-scientific-notation i get 15511210043330986000000000 but its not same as my actual output — Nitesh singh, Aug 15 '15 at 20:21
Possible duplicate of [factorial of a number](https://stackoverflow.com/questions/4438131/factorial-of-a-number) — Rich, May 02 '18 at 17:13

score 4 · Answer 1 · answered Aug 15 '15 at 21:27

In JavaScript, numbers have insufficient precision to represent all the digits of 25!, so simply calculating 25 * 24 * ... * 1 will yield an incorrect result.

To work with large numbers, the best approach is to use an arbitrary-precision integer library, like BigInteger.js, that's been thoroughly tested. But even if you can't use a library, you can still calculate 25! by breaking the result into smaller chunks:

function factorial(n) {
    var x = [1, 0];     // Two chunks are enough to represent 25!
    var base = 1e18;    // Each chunk x[0] and x[1] stores a number from 0 to (base - 1).

    function pad(i) {   // Pad a chunk with 0's on the left to 18 digits.
        return (i + base).toString().substr(1);
    }

    function trim(s) {  // Remove all leading 0's from the string s.
        return s.match(/[1-9].*/)[0];
    }

    for (; n > 1; n--) {
        x[0] *= n;
        x[1] *= n;
        if (x[0] >= base) {
            var carry = Math.floor(x[0] / base);
            x[1] += carry;
            x[0] -= carry * base;
        }
    }

    return trim(x[1].toString() + pad(x[0]));
}

console.log(factorial(25)); // 15511210043330985984000000

Note that this code does the bare minimum to calculate 25!. For larger values of n, more chunks need to be added.

score 4 · Answer 2 · answered Oct 01 '20 at 02:50

4

You can use BigInt in a recursive function like so:

 const factorialize = (num) => {
   if (num === 0n) return 1n;
   return num * factorialize(num - 1n);
 };
 console.log(String(factorialize(BigInt(25))));

answered Oct 01 '20 at 02:50

Penny Liu

15,447
5
79
98

2

The most elegant and easy to ready solution so far. Bravo! – konsalex Jan 22 '21 at 09:22

user3807877 · Answer 3 · 2015-08-15T19:50:12.997

if you want that kind of output you need to use a library that handles numbers differently than Javascript does. It's called BigNumber.js

your code would look like this:

function processData(input) { console.log(fact(input).toFormat().replace(/\,/g, "")); }
function fact(input) {
    if(typeof input != "object")
         input = new BigNumber(input);
    if(input.equals(1) || input.equals(0))
         return input;
    return input.times(fact(input.minus(1)))
}

score 2 · Answer 4 · answered Aug 06 '20 at 17:53

2

You can use BigInt:

console.log(BigInt(Array.from(Array(25),(_,i)=>BigInt(i+1)).reduce((a,b)=>BigInt(a)*BigInt(b))).toString());

answered Aug 06 '20 at 17:53

Vicky Gonsalves

11,593
2
37
58

How to find factorial of 25 in javascript

4 Answers4